[Stoves] venturi system -ratios of air and gas?

[Paul Medwell]

Dear Crispin,

I wonder if you can explain why a propane (C3H8) flame is not likely to 
be premixed, but a natural gas (CH4) flame probably is?

Regards,
Paul

On 9/1/16 1:55 AM, Crispin Pemberton-Pigott wrote:
> Dear Investigators
>
> What is the analysis of the propane that you consider 'typical'?
>
> If you can suggest a C, H, O % by mass, I can tell you the volume based on
> whatever excess air requirement you think is necessary.
>
> It is likely that a propane flame is not premixed. A natural gas flame
> probably is. Being pre-mixed doesn't mean it is 100% supplied, only that it
> is an aid-enriched gas mix that is depending on available air near the flame
> to complete combustion.
>
> I have some LPG formulations kicking around from India, South African and
> Nigeria. More important for the calculation below, what do you think the
> mass factions are?
>
> Regards
> Crispin
>
> -----Original Message-----
> From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
> Frans Peeters
> Sent: Friday, January 08, 2016 08:14
> To: 'Discussion of biomass cooking stoves' <stoves at lists.bioenergylists.org>
> Subject: Re: [Stoves] venturi system -ratios of air and gas?
>
> Andrew ,
>
>      You have better air 22% ? then we have ....20% means 10 vol air for 1
> mol propan .
>
> -----Oorspronkelijk bericht-----
> Van: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] Namens
> ajheggie at gmail.com
> Verzonden: vrijdag 8 januari 2016 11:39
> Aan: Discussion of biomass cooking stoves
> Onderwerp: Re: [Stoves] venturi system -ratios of air and gas?
>
> [Default] On Fri, 8 Jan 2016 00:31:19 +0100,"Boll, Martin Dr."
> <boll.bn at t-online.de> wrote:
>
>> A happy New Year to all stovers!
>>
>> In a venturi system like of a propane gas-burner the driving gas has
> pressure about 30 to 50 millibar.
>> - What ratio have the volumes of gas and air, to make our admired blue
> flame, as it does in gas-flames?
>
> As you thought it is a bit more complicated, the stoichiometric (chemically
> exact amounts to react for complete combustion) mass ratio of methane (same
> principle for propane but numbers are simpler) and oxygen is about 4:1 but
> as you have to allow for the other constituents of air, principally
> nitorgen, this means you actually have to supply about 17 kg of air for
> every 1 kg of gas.
>
>
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